Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$13.82	6.614%	$14.7341	$14.73	$14.75	$14.70
Purchase #2	$189.31	3.608%	$196.1403	$196.14	$196.15	$196.10
Purchase #3	$244.80	13.468%	$277.7697	$277.77	$277.75	$277.80
Purchase #4	$105.26	9.189%	$114.9323	$114.93	$114.95	$114.90
Purchase #5	$72.90	8.204%	$78.8807	$78.88	$78.90	$78.90
Purchase #6	$134.79	3.297%	$139.234	$139.23	$139.25	$139.20
Purchase #7	$147.99	11.623%	$165.1909	$165.19	$165.20	$165.20
7 purchase totals =	$908.87		$986.8820	$986.87	$986.95	$986.80